Documents may be scanned by a digital scanner in which a plurality of photosensitive devices are arranged to sense light reflected from a document to produce an electronic output indicative of the intensity of the sensed light. In a simple arrangement, documents are placed on a transparent imaging support platen and relative movement between the sensors and the document is provided, simultaneously with illumination of the document.
As used herein, the direction of relative movement is referred to as a slow scan direction while the direction of electronic acquisition of data is referred to as a fast scan direction.
It is common practice to provide a platen cover in association with the imaging platen to sandwich the document into a fixed position on the imaging platen and to prevent intrusion of extraneous light. Generally, the platen cover portion is placed adjacent the platen and is colored to provide a uniform background.
It is often a problem with the output of digital scanners; either at soft displays, such as video display terminals, or in printed samples of the scanned information; that the scanlines are not exactly parallel in the fast scan direction, or the images do not properly line up in the slow scan direction. This problem arises when a document is not properly registered with the scanning system; i.e., the document is not in the proper skew orientation or the proper orthogonal orientation.
Conventionally, it has been difficult to provide precise registration so that the document to be scanned is scanned at the desired skew orientation because the image may not have been placed squarely on the document, the edges on the document may not be squared causing the image to be skew on the registration of an edge, the sensor may not be registered properly with the platen, or the operator may not have precisely placed the document at the correct registration position on the platen. All these situations may result in a skewed image.
To realize precise registration for a digital scanner and ensure proper image quality, several conditions must be met. The nature of these conditions are illustrated in FIG. 1.
One condition is that the digital scanner must have proper fast scan registration. Proper fast scan registration is realized when an optical center line 5, as illustrated in FIG. 1, and a first pixel of a photosentive array are a known distance from a registration edge 2. If the optical center line 5 and first pixel are a known distance from the registration edge 2, the digital scanner will be able to provide precise fast scan registration.
Another condition of proper registration for a digital scanner is skew. To avoid unnecessary skew, the optical center line 5 must be parallel to the registration edge 2. Moreover, the pixels of the photosentive array (the fast scan direction) represented by image line 7 of FIG. 1 must be perpendicular to the registration edge 2 to prevent the skewed images. Thus, if the optical center line 5 and image line 7 of FIG. 1 meet the specifications discussed above, the images produced by the digital scanner should not be skewed.
A third condition of proper registration for a digital scanner is the placement of the document. More specifically, the document being scanned by the digital scanner must be placed relative to the registration edge 2 of FIG. 1 in a known manner. This is especially important when a document handler is utilized for the placement of a document on the platen platform. The placement of the document by a document handler on the platen platform should be predetermined in order for the digital scanner to known the relevant placement of the document to the registration edge.
Conventionally, to ensure proper registration for a digital scanner, a variety of adjustments in the actual manufacturing and setup of the digital scanner were utilized to meet these conditions. These adjustments were not only to the optical system, but to the registration edge and document handler as well. Such adjustments require additional manhours which significantly add to the cost of manufacturing a digital scanner. More specifically, the various components of a digital scanner were put together, and then a technician, at the manufacturing or customer site, would make manual adjustments to the assembled device so as to ensure proper registration for the digital scanner. Such reliance on manual adjustments after assembly increases labor and tooling costs for the manufacturing of a digital scanner. Moreover, manual adjustments to rails, optical carriages, and document handlers can be time consuming and labor intensive.
Therefore, it is desirable to be able to assemble a digital scanner without requiring extensive manual adjustments in order to assure proper registration.